Force plug for molded articles



Sept. 22, 1959 L. "r. CRABBE FORCE PLUG FOR MOLDED ARTICLES Filed Jan.31, 1956 INVENTOR L. 7. CRABBE 1 3%, m, mm W ATTORNEYS United StatesPatent FORCE PLUG FOR MOLDED ARTICLES 7 Lindsay T. Crabbe, Hinsdale,Ill., assignor to Phoenix Metal Cap Company, Inc., Chicago, 111., acorporation of New York Application January 31, 1956, Serial No. 562,437

1 Claim. (Cl. 18-45) This specification relates to a novel force plugused in the formation of molded articles such as bottle caps.

Molded bottle caps for screw-threaded attachment to bottles or similarcontainers are generally provided with sealing liners which fit againstthe mouth of the bottle. Retaining the liner in position for sealingpurposes in- I volves a particular formation of the cap. Primarily theliner must be inserted within the inner diameter of the screw-thread.Attachment of the liner to the cap can be made by means of adhesive.This, however, imposes a limitation on speed of assembly. Moreover, theadhesive may not be fully effective, but will deteriorate by standingand later fail to hold at the time when it is desired to remove the sealwith the bottle cap. Under such conditions the attachment of the seal tothe cap may be broken and the seal remain on the bottle mouth from whichit may have to be forcibly pried off by a separate operation.

It is of course well known to provide inwardly extending projectionswhich engage the edge of the liner and force it is not only to grip theinner surface of the cap, but also to rotate with the latter.

In respect to the method of forming the improved bottle cap, one'purpose of the invention is to utilize the inherent elasticity andresilience possessed by the thermosetting or the thermoplastic materialof which the cap is molded. These properties are temporary and last onlywhile the cap is in the formative stage and in heated condition. Theinvention therefore takes advantage of the fact that while still'heated, the molded cap can be stretched out of normal shape tofacilitate the removal of the retaining lugs without damaging them.Subsequently the cap returns to its normal shape. Finally the coolingoperation makes the cap rigid. At the same time there is a definiteshrinkage of the material resulting in reduction of the diameter of thecap.

A material incident in the novel method of forming the improved cap isthe provision of a force plug. This is used to form the inner surface ofthe cap during molding. The lugs for retaining the liner are formed byappropriate recesses in the side wall of the force plug.

Removal of the still plastic cap from the force plug by unscrewingimposes a strain upon the lugs which may cause damage to them. In orderto prevent this happening, the force plug is given a :novel shape inthat the recesses forming the lugs are extended on the leading side withrespect to the unscrewing operation, so that a gradual incline or slopeis provided. In this way the individual lugs are caused to move out ofthe recesses gradually, transferring the strain to the still plasticside wall of the cap without imposing damaging strain to the lugsthemselves.

An important feature of the force plug is that the lugforming recessesare in a plane spaced from and parallel to the upper surfaces. In thisway partial rotation of the still plastic cap not only causes each lugto ride up out of the forming recess, but also by reason of the pitch ofthe screw-thread, the lug is moved axially of the plug so The objects ofthe invention as above briefly pointed out and other incidentaldesirable features are shown by the following description and theaccompanying drawings of the preferred form of the invention in which:

Fig. 1 is a longitudinal cross-section of the improved molded cap withits liner;

Fig. 2 is a transverse cross-section of the cap taken on the line 2--2of Fig. 1;

Fig. 3 is a side elevation of the force plug used in molding the cap; A

Fig. 4 is a transverse cross-section on the line 4-4 of Fig. 3 and VFig. 5 is a similar fragmentary cross-section of the plug and capin theseparating operation.

Briefly described the invention utilizes the characteris tic features ofthe thermosetting or thermoplastic molding materials to form a row oflenticular lugs in a plane which will coincide with the inner surface ofthe seal. The seal may thus be snapped into position and held againstinadvertent removal. At the same time the seal is reasonably free to beheld by the mouth of the bottle in sealing relation while the cap isunscrewed up to the point where the upward pressure of the lugs is'suflicient to break the seal and thus lift the liner away from the mouthof the bottle.

To successfully form such a molded cap with retaining lugs it isnecessary, however, to provide a gradually sloping edge for the lugs sothat they may ride up out of the forming recesses. In this operation theelastic material will cause temporarily the deformation of the cap.

After removal of the cap from the force plug, the resilient plastic capresumes its normal shape. As the cap cools, it undergoes a definiteshrinkage into its final crosssectional dimension.

As illustrated, the bottle cap 6 is made of thermoplastic moldingmaterial. This cap is formed by molding the hot material under pressureinto the desired form over a force plug. As pointed out above, thethermosetting or thermoplasitc material is capable of limited stretchingwhile still hot, enabling its removal from the force plug. It hasinherent resilience, however, that brings it back to the normal moldedshape. Ultimate cooling of the article results in rigidity. At the sametime there is a characteristic shrinkage which necessitates removal ofthe cap from the force plug before cooling has progressed too far.

The bottle cap has an internal screw-thread 7. The valley 8 of thescrew-thread forms the channel which will receive the screw-thread onthe neck of the bottle or like article.

There is an inner top surface 9 for the cap. This may have a centralrecess 10 which limits the operating surface to a marginal flange 11. Aliner 12 is adapted to be held in place against the flange 11. The lineris customarily made of paper pulp, cork or the like, having a lowersealing surface.

The liner is held in place by means of lugs 13 integrally formed on theinner side wall of the cap. These are in a plane parallel to the flange11 and spaced far enough to receive the liner 12 as shown in Fig. 1.

The lugs 13 permit the liner to be snapped past and into place. Inposition the liner is retained but capable of relative rotation withrespect to the cap. It is thus possible for it to form a sealingengagement with the mouth of the bottle subject, however, to beingpulled away by the pressure of the lugs on the inner face of the liner.

Patented Sept. 22, 1959 The lugs 13 are formed integrally with thebottle cap 6 during the molding operation by the use of a special forceplug 14. This force plug is made of steel or other similar material and:is generally cylindrical in form. It r.

convex. sides. The center line which forms the edge of the lugs slopesdown toward each end. Therear end 13 is substantially the same radius asthe cutting tool; The front edge 19 is given a more gradual slope thanedge 18.2 This is accomplished by moving the cutter or grindercircumferentially of the plug and at the same time withdrawing it.

This results in giving the same general contour to the individual lugsduring the molding operation. Thus each lug 13 will have a front edge 20of gradual slope and a rear edge 21 more abrupt in slope. This isindicated particularly in Figs. 2 and 5, while the gradual slope of thefront edge of the recess 17 is clearly shown in Figs.- 3 and 4.

During the molding operation the force plug 14 operates-upon a mass ofheated thermosetting or thermoplastic material in the mold to form thecap 6 with its screw-thread 7 and the lugs 13.

While the material is still hot and plastic, the cap is unscrewed byrotation counterclockwise, as shown in Fig. 5. This is made possible bythe fact that the material is still capable of being stretched.

In this movement each individual lug 13 rides up the Each recess islenticular in that it has slightly more gradual slope of the edge 19 ofthe recess 17.

The-lug is therefore brought out onto the cylindrical side surface ofthe plug without deformation or damage; such 4 erally of the nextsuccessive recess 17 Slight continued rotation of the cap will lift itup of the force plug without damaging the lugs.

After separation from the force plug, the cap by reason of its resilientmaterial will resume the normal crosssectional form as shown in Fig. 2.The cap as it cools will also shrink into the ultimate, desiredcross-sectional dimension. I

The particular form of the lugs is thus most advantageous in permittingtheir 'formationintegral -withthe-'=-" cap-without likelihoodof-deformation or damagew; The inner wall of the cap which carries thelugs "also has a diameter not greater thanv the root of the screw-thread15 (rib of the screw-thread 7). As a consequence, the liner 12 willreadily pass the screw-threaded portion of the cap and be easily movedinto position above the series of lugs. It is thus held againstseparation, but permitted relative rotary motion, so that the seal onthe-bottlezor the like remains untilthe series oflugsforcibly lift-the*1 liner off the mouth of the bottle.

While the preferred formof the invention has been described above indetail, numerous variations in form,

material. and proportions are possible without departing from the scopeof the following claim.

What I claim is:

A force plug for molding a thermosetting or thermoplastic bottle tophaving a generally cylindrical form,

a screw-thread on the side wall and a transverseseries of lenticularrecesses. on the said side wall above the end of the screw-thread, eachof said recesseshaving its edge nearer the screw-thread with aslope'less than that Y of the opposite edge.

References Cited in the file of this patent UNITED STATES PATENTS Re;19,000 Scribner Nov. 14, 1933 2,039,757 Von Till May 5-, 1936' 2,130,749Von Till Sept. 20, 1938 2,175,350 Hammer Oct. 15, 1939 2,312,513 WilsonMar. 2, 1943. 2,317,823 Strauss Apr. 27, '1943

